Theresa May might have saved her job by declaring to Conservative MPs that she will not lead the party into the next general election, but she risks turning herself into a lame duck prime minister.
It has long been a political convention that prime ministers do not announce retirement plans in advance, for fear that the remainder of their term in office will be dominated by speculation over their successor.
Attention can now be expected increasingly to focus on whether senior Tories are preparing a bid for the leadership.
And tying her future departure to the delivery of Brexit will inevitably raise questions about whether Mrs May intends to remain in place until the official date of the UK’s withdrawal in March 2019, the end of the agreed transition period in December 2020 or the end of a possible extended transition in 2021 or 2022.
Labour MPs immediately seized upon Mrs May’s comments to suggest that she could not remain long in 10 Downing Street.
“Even if she wins, this duck is lame,” said former minister David Hanson.
And Chesterfield MP Toby Perkins said Mrs May was “safe for another year” only.
Tony Blair broke the taboo in 2006 when he announced he would quit within a year, after coming under intense pressure from his chancellor and rival Gordon Brown to hand over the reins of power.
In fact, the Labour PM lasted only another nine months, having faced continued pressure from media and politicians to name a precise date for his departure.
David Cameron declared just weeks before the 2015 general election that he would not seek a third term if re-elected as Conservative prime minister.
The shock announcement sparked immediate speculation about exactly when he would quit and whether he would give a successor time to establish him or herself before the next poll, which was then expected to come in 2020.
In the event he did not have a chance to quit at a time of his choosing, instead resigning on the morning after losing the 2016 EU referendum.